This invention relates in general to reducing machines, and more particularly to a reducing machine having a cage which is positively displaced both toward and away from the rotor of the machine.
Coal as it is taken from the mine is primarily in lump form, with the lumps being much too large for use in stokers and coal burning equipment. Usually, the coal is passed through a reducing machine, called a coal crusher, to reduce it to uniform size suitable for use in coal burning equipment.
The typical coal crusher has a housing and a rotor which revolves in the housing. The rotor carries breaking elements which strike the coal and reduce it in size. The housing also contains a cage which is below the rotor, and this cage is provided with a screening device through which the reduced fragments of coal will pass when they reach the desired size.
In the course of operation the coal tends to clog the openings of the cage screen, and it is therefore desirable to have the cage drop downwardly so that it may be cleaned. Indeed, it is common practice to clean such screens at least once a day. When the coal contains mud, the cleaning must occur more often. Not only does the drop-type cage facilitate cleaning, but it also enables the machine to be cleared of coal prior to start up. In this regard, sometimes coal from overhead conveyors and chutes will migrate into idle machines and will accumulate on the screens thereof. However, the machines cannot be started under load, and hence must be completely cleared of the accumulated coal. The drop cage also enables the screens to be replaced with relative ease. Finally, the mechanism for dropping the cage affords a convenient means for adjusting the vertical position of the screen so as to compensate for wear of the breaking elements on the rotor. It also provides some control over the size of the coal fragments which are discharged through the screen.
Machines of current manufacture have cages which are suspended from chains passed over sprockets. The chains enable the cage to be dropped a substantial distance below the bottom of the machine so that convenient access to the screen and to the interior of the machine is available. The chains further exert an upwardly directed force on the cage so that it may be raised and held in a desired position beneath the rotor. However, the chains do not exert a downwardly directed force on the cage. Hence when the chain is released, the cage usually drops downwardly under its own weight, but sometimes coal and mud cakes between the cage and housing and holds the cage upwardly after the chain is released. When this occurs a force must be applied to the cage from within the machine, and this may be a time consuming and somewhat difficult procedure.
Heretofore machines have been developed with positive cage displacement in both directions, but the mechanisms utilized in these machines for moving their cages do not enable the cages to be dropped to near the extent possible with a chain suspension system.